Conventional solid fuel-fired boilers include, for example, a pulverized coal-fired boiler which burns pulverized coal (coal) as a solid fuel. There are two types of known firing systems in such a pulverized coal-fired boiler: a circulating firing boiler and an opposed firing boiler, both of which require warming-up operation before combusting a solid fuel.
Of these systems, the circulating firing boiler has oil-fired burners for boiler warming installed above and below a pulverized coal burner (e.g., see PTL 1).
The above-mentioned oil-fired burner is, for example, as in the configuration example shown in FIG. 5, arranged in the order of a secondary air input port 51, an oil-fired burner 30, a pulverized coal burner 52, an oil-fired burner 30 . . . a pulverized coal burner 52, and an auxiliary air input port 53, from the upper stage in the front view of a wind box 50 taken from the inside of a furnace. Thus, multiple pairs of the oil-fired burner 30 and the pulverized coal burner 52 are combined in the vertical direction to serve as an integrated unit which is continuous in the height direction of the furnace.
The above-mentioned oil-fired burner 30 has, for example, as shown in FIG. 6, a rectangular leading end of a nozzle main body 31 (rectangular cross-section of the main body) when viewed from the inside of the furnace, and a nozzle tip 32a of an oil gun 32 for inputting fuel oil by injection is disposed at the center of an outlet opening. Inside the nozzle main body 31, a secondary air input port (nozzle) 33 is provided so as to surround the outer periphery of the nozzle tip 32a which is substantially circular in cross-section. This secondary air input port 33 has a rectangular shape which is substantially the same as the shape of the leading end of the nozzle main body 31, but is somewhat reduced in the vertical direction so as to be somewhat smaller in opening area than the nozzle main body 31.
Reference numeral 34 of FIG. 6 denotes a substantially conical diffuser which is formed around the nozzle tip 32a, and a cylindrical ignition air passage 35 is provided so as to surround the outer periphery of the diffuser 34.